stocking and algea problem

[ajm]

I have a 55 gallon that is pretty well established water tests/tested fine and I mysteriously lost a clown within a few days of his "problem" starting (looked like his lip/mouth was rotting away), bought a nice sized eel and he decided to jump out of the tank not even 24hours after buying him, then I had been having trouble with my lion eating and today he was gone. Ive had him for about 3 months. He had been doing GREAT eating frozen foods. All of the sudden he just wanted to stop eating water and everything tested fine, he still kept on refusing to eat and today when I woek up he was dead. So im looking to restock but this time im looking for something thats more of a "community tank" and was wondering if anyone had some suggestions. They must be quite "cheap" as well. Im going to school full time and my parents are paying for everything so they wernt happy to hear a $70 fish I got 3 months ago died and arent lookin foward to spending more.

Second thing my tank has been taken over by what seems to be a brown algea? Basicly just brown film like crap EVERYWHERE, glass,substrate,LR,artifical lava rock, you name it everything as this stuff on it. Is there a simple way to get rid of it while I have no fish in the tank such as raising the salanity & temperature. Thanks.